71 



Dr. Farrington reported a complete disappearance of this species from 

 his vicinity, and Prof. M. V. Slingerland, who has studied the species 

 in New York, noted a similar lack of injury in the neighborhood of 

 Ithaca, N. Y. 



PROBABLE EXPLANATION OF THE INSECT'S DISAPPEARANCE. 



To explain this disappearance the following reasons present them- 

 selves. Assuming the natural time for the appearance of the flies in 

 the District of Columbia to be toward the end of May or first of June, 

 the weather that was encountered during 1903 at this time was unusu- 

 ally cool and will doubtless explain the practical extirpation of the 

 species temporarily and locally. In other localities similar adverse 

 atmospheric conditions prevailed which might have produced the same 

 effect. A cold wave was experienced in the latitude of Washington 

 in the last week of April, causing some loss to early vegetable growth. 

 During the third week frosts were prevalent, which also had a damag- 

 ing effect "on susceptible crops. Frosts also occurred during the last 

 week of April. In short, the spring was late for this section. The 

 first three weeks of May showed drought in many sections, and fre- 

 quent temperatures from 85° to 90°, and nearly 100 during the third 

 week, the end of the month turning cloudy and cool, after which 

 showers were of almost daily occurrence, accompanied by thunder, 

 hail and high winds, these conditions continuing practically through- 

 out the entire month of June. a That undue dryness usually causes 

 retardation in development is an established fact, hence there is little 

 doubt that the dry weather had the effect of preventing the meta- 

 morphosis of this species, until frost and dampness ensued at exactly 

 the time when the fly should have issued from its puparium, with the 

 result of its destruction in great numbers. 



EARLIER RECORDS OF INJURY. 



July 17, 1899, we received the same species from the Hittinger Fruit 

 Company, Belmont, Mass., then in the larval condition, with state- 

 ment that cherries there were very generally affected. 



During the same year, as also in 1900 and 1901, this species attracted 

 considerable attention at Ithaca and Geneva, and elsewhere in New 

 York, as recorded by Professor Slingerland in Bulletin 172 of the 

 Cornell University Agricultural Experiment Station. This simul- 

 taneous outbreak of a species hitherto unrecognized as noxious in New 

 York, Massachusetts, and the District of Columbia is quite remark- 

 able. A reported case of injury in northern Michigan in 1889, just 

 ten years earlier, is attributed to this species, and probably correctly 



a See Weekly Crop Bulletin, Maryland and Delaware Section, Climate and Crop 

 Service of the Weather Bureau, of this Department. 



